Uranus: 2003 (Unannotated)

Even though the Voyager 2 spacecraft paid a close-up visit to Uranus in 1986, the distant planet continues revealing surprises to the eye of NASA's Hubble Space Telescope. Hubble’s high sensitivity and sharp view has uncovered a pair of giant rings girdling the planet. The largest is twice the diameter of the planet’s previously known ring system, first discovered in the late 1970s. Hubble also spied two small satellites, named Mab and Cupid. One of the satellites shares an orbit with the outermost of the new rings. The satellite is probably the source of fresh dust that keeps replenishing the ring with new material knocked off the satellite from meteoroid impacts. Without such replenishment, the dust in the ring would slowly spiral in toward Uranus. Collectively, these new discoveries mean that Uranus has a youthful and dynamic system of rings and moons. Because of the extreme tilt of Uranus's axis, the ring system appears nearly perpendicular relative to rings around other gas giant planets like Saturn. Also, unlike Saturn, the rings are very dark and dim because they are mostly dust rather than ice.